1. Field of the Invention
The invention is directed to a fluorescent foil or film, particularly for use with a low-pressure discharge lamp, a method for producing the fluorescent film and an irradiation arrangement with the fluorescent film.
2. Description of the Related Art
Light absorption through the skin causes tissue changes by influencing the neuronal, lymphatic, vascular and immune systems. This brings about analgesic, antiinflammatory, antiedematous effects and stimulates healing of wounds. A considerable increase in fibroblasts of scar tissue was found under irradiation by red light (660 nm, 2.4-4 J/cm2) (C. Webb; M. Dyson, et al., Lasers in Surgery and Medicine, 22(5), 294-30, (1998)). When peripheral lymphocytes were irradiated by an He-Ne laser with irradiation doses of between 28 and 112 J/m2, there was an increase in RNA synthesis after stimulation of the lymphocytes by cytohemoagglutinin (N. K. Smol'yaninova, T. I. Karu, et al., Biomedical Science, 2(2), 121-126 (1991)). With bone injuries, a doubling of calcium incorporation at the injury site was observed after He—Ne laser irradiation (T. Yaacoby, L. Maltz, et al., Calcified Tissue International 59(4), 297-300, (1996)). Various chronic joint diseases such as gonarthrosis, LWS arthrosis and algodystrophy in hemiplegic stroke patients were found to be positively affected by He-Ne laser irradiation in over 400 patients (S. Giavelli, G. Fava, et al., Radiologia Medica, 95(4), 303-309, (1998)). The release of interleukin-1-alpha and interleukin-8 has been discussed as a possible cause for the positive effects (H. S. Yu, K. L. Chang, et al., Journal of Investigative Dermatology, 107(4), 593-596, (1996)). Irradiation at 1.5 J/cm2 resulted in a concentration-dependent simulation of interleukin- 1-alpha production and corresponding mRNA expression. Since these cytokines stimulate both mobility and proliferation of keratinocytes, it is likely that these mechanisms directly promote wound healing. Further, models of photonic cellular energy transfer in relation to the respiratory chain are being discussed (L. Wilden, R. Karthein, Journal of Clinical Laser Medicine and Surgery, 16(3), 159-165, (1998). The biochemical models of cellular energy transfer take into account only the typical corpuscular aspect of electrons as responsible for energy transfer and ignore the wave-particle dualism of electrons in energy transfer. The light of the red and near-infrared spectra closely corresponds to characteristic energy planes and absorption rates of important components of the respiratory chain. For example, an increase in mitochondrial adenosine triphosphate production is brought about in this way. Interactions in the red and near-IR ranges can be explained on the basis of this interaction.
Photobiological effects in the non-UV range based on an interaction between endogenic or exogenic chromophores in the skin are becoming increasingly important because therapeutic effects can be influenced by means of suitable radiation sources in certain inflammatory skin diseases and, for example, impairment of wound healing in diabetes mellitus.
Because their efficiency is usually better than that of high-pressure lamps or temperature radiators, low-pressure discharge lamps are used increasingly in many technical fields, especially when high light energy efficiency is required. Single-base or double-base low-pressure discharge lamps are known depending on the field of use. Further, these low-pressure discharge lamps can be constructed with or without luminescent material and with different gases. However, all embodiment forms have in common that the light energy transfer increases as the diameter of the enveloping body decreases.
According to one model calculation, the light energy density corresponds to approximately one fourth of the quotient of the column capacity and projection surface. This means that the theoretical maximum value of a 38-mm low-pressure discharge lamp is approximately 45 mW/cm2. In a 26-mm low-pressure discharge lamp, the light energy density increases to approximately 50 mW/cm2. Theoretical light energy densities of 100, 125 and 170 mW/cm2 result for lamp diameters of 16 mm, 12 mm and 8 mm. The increased luminous density of small radiators is utilized, for example, in the construction of compact lamps having, e.g., a wall diameter of 12 mm. Fluorescent tubes with a diameter of 8 mm have been in use for some years for effect illumination. They surpass compact lamps with respect to luminous density, but the greatest available lengths are only about 30 cm.
In spite of the increased light output, however, the reduction in lamp geometry has grave disadvantages. A large number of lamps with an equally large number of expensive ballast devices are required in order to generate radiating surfaces. The lengthening of the lamps is subject to plasma-physical limits because the high ignition voltages that are required for large lengths represent a considerable expenditure. Added to this is the manufacturing cost itself, i.e., elutriation, pumping and basing of each individual fluorescent tube.
Therefore, low-pressure discharge lamps with external or internal reflectors are usually used for surface illumination; for example, light energy densities of between 22 and 28 mW/cm2 at an irradiation level of 100 W can be achieved. However, the light energy densities that can actually be achieved are considerably lower than in theory.
The basic problem in conventional low-pressure discharge lamps with fluorescent material and electron-emitting electrodes is the limited period of use, especially with very high lamp outputs.
The principal reason for this is that reaction components of the electrode burnup react chemically with the luminescent coating, which leads to an aging process. Another problem is that the reaction components of the electrode burnup and of the mercury vapor react with alkaline compounds of the glass tube to form various amalgams. This results in blackening of the tube, accelerated reduction of light output and sometimes in a dramatic reduction in the useful life of the lamp. Since the useful life is already sharply limited due to the aging process of the luminescent coating, the use of expensive alkali-free fused silica glasses has so far been unprofitable. For medical high-power radiators, the useful life may only amount to 48 hours, for example.
Experimental application of luminescent material to the outside of the low-pressure discharge lamp was not successful because the application of luminescent material in a non-inert atmosphere leads to a photochemical oxidative degradation of the hygroscopic luminescent material.
U.S. Pat. No. 5,717,282 discloses a Braun tube for monitor production in which a silica-containing paint with luminescent materials which is produced by a sol-gel process is applied to the outer side of the monitor. The thickness of this phosphor coating is limited to about 0.5 μm because, otherwise, cracks would result from the extensive shrinkage of the inorganic network. However, a layer of this thickness is too thin and does not have sufficient thermal stability for use in a low-pressure discharge lamp at higher outputs.
U.S. Pat. No. 5,731,658 discloses a liquid crystal display in which a phosphor coating is applied to the inner boundary walls. The phosphor coating comprises a UV-transparent carrier material and phosphor. Silicone oxide or organosilicates, particularly ethyl silicate, methyl silicate or isopropyl silicate, are suggested as carrier materials. The coating thickness that can be achieved in this way is also too small to allow for adequate embedding of luminescent material for a low-pressure discharge lamp.